Forward osmotic and water hammer method of membrane cleaning

ABSTRACT

Apparatus and method for semi-permeable membrane cleaning in particular, applying series of pulsed water stroke, made simultaneously with osmosis backward flow causing superposed membrane directional shaking and fouling detachment. Pulsed water stroke provided by water stroke generator as several momentum sharp changes in gauge pressure and induce velocity pulse of residual brine flow. The pulsed water strokes ideally induce resonance in the membrane. Osmosis backward wash may be provided either by injection for predetermined injection time, additional solution selected in such way that net driving pressure becomes opposite to normal osmotic operation thereby providing a backward flow of permeate towards to the side opposite to normal operation mode, so as to lift said foulant, or by throttling permeate exiting from the permeate enclosure, until the net driving pressure value become equal to zero, during application of precise synchronized and opposing brine and permeate pressure strokes thereby providing a plurality of quick RO-FO-RO process changes. These procedures allow a membrane to be kept continuously clean and operate at higher recovery.

This application claims the benefit of Great Britain patent applicationNo. 1414263.2, filed Aug. 12, 2014, and Great Britain patent applicationNo. 1501243.8, filed Jan. 26, 2015 which are hereby incorporated byreference in their entirety.

FIELD OF THE INVENTION

The present invention relates to a method and system for cleaningsemi-permeable membranes used in Forward Osmosis and Reverse Osmosisprocesses, such as those implemented in desalination of sea, brackish,wastewater, food processing, pharmaceutical industry, high purityapplication, osmotic power generation, waste water treatment and etc.

BACKGROUND OF THE INVENTION

Semi-permeable membranes become fouled spontaneously during normaloperation process and conditions through the accumulation of foulingmedia. A fouled membrane has a reduced separability of the dissolvedsalts, a reduced flux rate, an increased pressure loss and, therefore,has to be cleaned.

Fouling media includes minerals and organic particles, scalingmicrocrystals, bacteria, and algae. All these components are containedin a biofilm matrix made by bacteria. There are no free particles on themembrane surface. All the fouling elements are interconnected by thebiofilm. Therefore, fouling is characterized as a layer ofinterconnected elements laying on a membrane surface as a carpet. In thebiofilm matrix exists the most concentrated part of feed solution, whichis called and causes Concentration Polarization. In this invention, theterm “fouling” includes all of the different forms of fouling asmentioned above or known to the skilled man in the art.

The fouling may be located on the feed or the permeate membrane sides.However, most of the fouling is located on the feed membrane side. Dueto the membrane structure, the thickness of the fouling biofilm is notequal over the entire surface of the membrane.

A permeate spacer is a grid of solid fibers, defining semi-rectangularvoid spaces. The permeate spacer is located between the permeate sidesof two opposing membrane layers defining a permeate channel. On top ofeach of such a semi-rectangular void space, there is a free membranelayer portion which may stretch down and displace toward the permeateside, a phenomena called sagging toward permeate side. This displacementtakes place because the gauge pressure on the feed side is higher thanthe gauge pressure on the permeate side. As a result, under thesecircumstances the membrane surface gets a wave-like profile in whichvalleys caused by sagging are located above the void spaces of thepermeate spacer and the hills are located on top of its fibers.Similarly, a feed spacer is usually located between two opposing feedsides of two opposing membrane layers defining a feed channel. The feedspacer is also a mesh of solid fibers which define void spaces.Typically, the void spaces of the feed spacer are bigger than the voidspaces of the permeate spacer. In the following description“displacement toward the feed side” or “feed forward sagging” means thatthe displacement toward the permeate side is diminished. In thefollowing description, a membrane may oscillate between a more displacedposition (sagged) toward the permeate side and a less displaced position(sagged) toward the permeate side. In a spiral membrane, this wave-likesurface dictates a feed flow regime along and across the membrane whichenhances the accumulation of more fouling media in the valleys areasthan in the hills areas. In these valleys areas the longitudinal flowvelocity is lower and more fouling media tends to accumulate.

Standard methods for membrane cleaning involve: stopping the ROdesalination process; disconnecting membrane modules from the highpressure pump; connecting the membrane modules to a Cleaning In Place(CIP) unit; pumping by a low gauge pressure harsh chemicals along thefeed membrane side. This CIP method is expensive, not effective, andcreates environmental problems.

U.S. Pat. No. 4,952,317, describes separating colloidal suspension bynon directional, tangential vibration of the membrane elements. Thisvibration induces the creation of intensive shear forces between themembrane and the colloidal suspension. Such a vibration treats andvibrates the membrane as a whole and does not distinguish betweenmembrane and spacers or between the feed channel and the permeatechannel.

This technique has to be applied continuously during the normaloperation of the membrane. However, continues vibration applicationconsumes significant power, and accelerates membrane wear and tear.However, as explained above the nature of the fouling in most of thecases is not a colloidal suspension nature, but rather a biofilm matrixbehaves as carpet/layer nature which tends to be attached to themembrane by adhesion forces. Tangential vibrating of the membraneelements having such a carpet layer of fouling adhered to the membranesurface cannot remove it. Therefore, it is one aspect of the presentinvention to provide a cleaning solution to remove a fouling layercharacterized by a carpet structure.

A known RO membrane Cleaning Method is disclosed in WO/2005/123232, alsoknown as “DOHS process”. This DOHS process teaches the implementation ofa cleaning method based on a temporarily inline injection of a SuperSaline Solution having a high osmotic pressure into the feed line, sothat the Net Driving Pressure across the membrane is locally andtemporarily reversed. As a result, the osmotic process over a membranearea switches from a reverse osmosis process to a direct osmosisprocess. Once the Super Saline Solution propagates downstream themembrane module, then the local osmotic pressure regime across themembrane is restored to its original values and the system then switchesback to a reverse osmosis process. This procedure is done withoutstopping the desalination unit, without releasing the gauge pressures inthe system and without inducing membrane sagging. It is mainly theosmotic pressure which is being changed and this cannot cause membranesagging. The invention further teaches that switching from a reverseosmosis process to a direct osmosis process provides intensive permeatebackward flow of permeate into the Raw Saline solution. The localbackward flow of permeate from the permeate side into the feed-brineside may clean the membrane.

Additionally, several patents and patent applications implement gaugepressure pulsation for membrane cleaning, such as US2011/0315612; U.S.Pat. No. 7,658,852 (B2); U.S. Pat. No. 5,690,829 (A); US2012318737 (A1);JP 2005238135 (A); U.S. Pat. No. 3,853,756 (A); U.S. Pat. No. 7,097,769(B2).

The intention of gauge pressure pulsation is to change the process fromreverse osmosis to forward osmosis. Generally, a pulse generator ispositioned in the feed stream and most of them implement high amplitudeof pressure pulsation, such as 30-60 bar. In permeate lines such bigamplitude request implement expensive pipe material and assembly work.Such a large amplitude of pressure change can be done by gauge pressurechanging velocity of not more than 10 psi per second. This means thatexpected frequency can be very small.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, this invention relatesto an apparatus and method for an improved membrane cleaning by applyinga plurality of directional gauge pressure strokes in the permeate orresidual brine stream in order to induce a plurality of membrane feedforward sagging pulses/displacements which shakes the membranemechanically and the fouling biofilm on top of it, during the sameperiod of time when the same membrane area experiences a permeatebackward flow induced by a FO process.

The present invention may be practiced in a normally performed ROprocess in which fouling is cleaned by injecting into the feed line anadditional solution having a higher osmotic pressure than the normalfeed osmotic pressure, creating a FO permeate backward flow. The presentinvention may also be practiced in a FO or PRO processes, in whichfouling is cleaned by injecting into the feed line an additionalsolution having a lower osmotic pressure than the normal feed osmoticpressure, creating a RO permeate backward flow.

A plurality or set of directional gauge pressure strokes may be createdby a generator of water stroke installed in residual brine stream. A Setof directional permeate gauge pressure strokes may be created by anexternal source of pressurized permeate. Such an external source ofpressurized permeate may be for example a pump, driving permeate fromexternal tank into the permeate enclosure. According to another example,a plurality of directional permeate gauge pressure strokes may becreated by a generator of water stroke which is configured to releaseand stop releasing permeate flow from a permeate enclosure. According toanother aspect of the present invention both a pump and a generator ofwater stroke may operate together, pumping additional permeate into thepermeate enclosure and discharging permeate from the permeate enclosure.

This invention is applicable to all types, and brand names of semipermeable membrane, including Reverse Osmosis (RO), Nano Filtration(NF), Pressure Retard Osmosis (PRO), Forward Osmosis (FO), DirectOsmosis (DO) and other brand name membranes, arranged as Spiral,Hollow-Fiber, Plate & Frame (P&F) and other construction or build fromdifferent salt rejection material already present on the market andnovel such as zeolite, carbon, nanostructured, mix matrix etc. All thesemembrane have common characteristic: Selective permeability to solventand solute. These membranes have a common name “semi-permeable membrane”and in the present invention, the term “membrane” includes all those andother known membranes to the skilled man in the art.

Some types of membrane elements such as Spiral and P&F have permeatespacer. Other types of membranes do not have support spacer and areselves-supported like Hollow-Fiber. The present invention is applicableto spacer-supported and self-supported membrane equally.

In nature, there exist two fundamental processes: Forward Osmosis andReverses Osmosis processes. In the present invention under the termForward Osmosis process (FO) are included Direct Osmosis (DO), Osmosis(OS), Pressure Retard Osmosis (PRO), and other known processes to theskilled man in the art in which a common physical phenomena takes placenamely solvent penetrates from low osmotic pressure solution viasemi-permeable membrane in to high osmotic pressure solution. In such aForward Osmosis process, the semi-permeable membrane acts as an osmoticpump.

In the present invention under the term Reverse Osmosis process (RO) areincluded all the processes in which solvent (permeate) is squeezed outfrom high osmotic pressure solution via a semi-permeable membrane byhydrostatic pressure that is higher than the osmotic pressure of thisraw saline solution. In such a Reverse Osmosis Process, thesemi-permeable membrane acts as a selective barrier.

Membranes usually have multi-layer structure. Semi-permeable layer isthe external layer. In RO applications semi-permeable layer usuallyorientated toward the feed side. In FO process applications,semi-permeable layer can be orientated to feed or permeate side. Thepresent invention may be applicable to each of these configurationsequally.

There are about 40,000 permeate channels in a typical spiral membraneelement, each channel has a typical dimension of an about 0.5 mm×1000mm.

Permeate channel consists of a gridded permeate spacer covered by asemipermeable membrane on both sides, which acts as a tight tensedrumheads over the void spaces between the grid. The free membraneportions stretch and displace over the void spaces existing betweensolid support fibers of the permeate spacer. Such a displacement ischaracterized by an elastic deformation caused due to the differencesbetween the feed gauge pressure, PGr, and the permeate gauge pressurePGp.

As mentioned above, the functionality of such a free membrane portionmay be switched from a solute-solvent separator in a RO process, to anosmotic pump in a FO process by injecting additional solution into thefeed brine channel in order to establish a temporal backward flow acrosssuch a free membrane portion. Reversing the net driving pressure acrossa membrane portion by temporarily switching the osmotic pressure regimeis enough to establish a backward flow. Such a backward flow may cleanthe membrane from fouling. However, since the fouling has the nature ofa biofilm layer which sometimes is strongly connected to the membranelayer, such a backward flow in some cases may be insufficient to detachthe fouling layer from the membrane layer. Therefore, according to oneaspect of the present invention, simultaneously with the establishmentof such a backward flow, a gauge pressure manipulating system isconfigured to create a plurality of directional water strokes, directedfrom the permeate channel to the feed brine channel or opposite.Preferably, sinusoidal pulsating the feed or permeate gauge pressureenhances the mechanical oscillation of the free membrane portion.

It is another aspect of the present invention to synchronize thebackward flow established by injection of the additional solution andthe gauge pressure stroke, so that the backward flow across the freemembrane portion and the feed forward sagging of this free membraneportion coincide. The accumulated effect of the backward flow and themembrane shaking improve the cleaning efficiency process of themembrane.

The propagating speed of the additional solution along the feed brinechannel depends on the feed flow, the number of membrane elements in amodule, and the number of module stages etc. The osmotic pressure of theadditional solution decreases while it propagates along the membraneelements due to a dilution caused by permeate flow into it. Injectionprofile, such as duration, volume or flow rate, of additional solutionhas to be selected in such a way that the last membrane element in thelast module will get sufficient net driving pressure allowing aneffective cleaning though backward flow.

According to one embodiment of the present invention, a pulse of 3seconds to 50 seconds of additional solution may be injected into thefeed-brine channel while a set of directional water pressure strokes isbeing generated simultaneously. According to one embodiment of thepresent invention, water pressure strokes may be generated before theinjection of an additional solution and may continue several minutesafter such an injection, until the system restores its original netdriving pressure balance across all membrane modules. According toanother embodiment of the present invention, residual brine outlet flowmay be increased while water pressure strokes are applied. This enhancedbrine flow may increase the longitudinal shearing forces along themembrane and further improves the membrane cleaning effect.

According to another preferred embodiment of the present invention,periodic oscillations of the pressure difference between PGr and PGp,may cause an oscillation of the free membrane portions. As a mechanicalsystem, under the situation of oscillating gauge pressures, thestretched free membrane portion over a void spaces between the solidgrids of fibers, is in a mechanical state characterized by a forcedvibration with damping. As such, the system has a single degree offreedom and therefore at least one natural frequency. However, asmentioned above, the permeate facing side of the membrane is supportedby a permeate spacer and the feed facing side of the membrane issupported by a feed spacer. During sagging vibrations, permeate and feedspacers act as a damping system. It is another preferred embodiment ofthe present invention to create gauge pressure strokes having afrequency approximately equal to at least one natural frequency of thesystem in order to get a resonance and enhanced displacement andtherefore an enhanced cleaning effect. An example of a natural frequencyof a brackish water spiral membrane, is about 2.5 Hz. Operation inresonance frequency allows by minimum gauge pressure amplitude reachmaximum membrane oscillation amplitude, which make cleaning process moresafely and cost effective.

Membranes oscillation in frequency proportional to their naturalfrequency may increase the amplitude of their vibration (resonanceeffect). Because the vibrations states in this system are such as withdampers, spacers' solid fibers will absorb some of the stroke energy. Apoint will come when the total energy absorbed by theses dampers willequal the total energy being fed in by the gauge pressure oscillation.At this point, the system will reach its maximum amplitude and willcontinue to vibrate at this level as long as the oscillation force staysthe same.

The present invention implements different approaches of membranecleaning in variety options of membrane mechanical shaking with andwithout resonance by means of PGp and/or PGr gauge pressure strokes andcombined with reversing osmotic processes from RO to FO.

It is preferable for the mechanical shaking of the present invention toprovide Resonance Membrane Oscillation. This is because the membrane isin contact with feed spacers acting as dampers and to reach membraneoscillation the gauge pressure change geometry has to have wave-likesmooth sinusoidal form including half-wave increase and half-wavedecrease gauge pressure. Pulse-like feed pressure decrease only, withoutproportional pressure increase, will not provide the required membraneresonance oscillation. Single pressure decrease or increase is not ableto cause resonance. Thus, according to the present invention, a set ofat least several sinusoidal water strokes is preferred to provide therequired resonance oscillation.

Furthermore, the positioning of the water stroke generator, has to takein the account extremely high elasticity of the membrane, small watermass in the membrane, sensitivity of the feed pump to pressure pulsationand the presence of a residual brine discharge outlet.

A control valve or other water stroke generator is positioned in thefeed stream between the feed pump and membrane to provide pressureincrease wave in direction of the feed pump, and pressure decrease wavein direction of the membrane. A control valve in the feed stream cannotprovide sinusoidal form of gauge pressure change that includes half-waveincrease and half-wave decrease gauge pressure on the membrane.

A water stroke generator poisoned to discharge the feed flow out fromthe RO system, such as in US2012318737 also will not be able to providesinusoidal form of gauge pressure change. In contrast, a control valveor other water stroke generator positioned in residual brine stream aspreferred in the present invention is able to provide sinusoidal form ofgauge pressure change that include pressure increase and pressuredecrease half-wave.

It is known to the skilled man in the art that the maximum allowed gaugepressure change velocity is 10 psi/second, [1]. However, our researchhas shown that, up to 45 psi/second oscillation will not damage membraneif the following conditions are fulfilled:

-   -   Gauge pressure change geometry has wave-like smooth sinusoidal        form.    -   Gauge pressure amplitude not more than ±3 bar, measured in feed        manifold pipeline to pressure vessels. In some cases it may be        limited to be below ±5% of the normal operation range.

In present embodiment of the invention the feed and/or permeate gaugepressure pulsation are small, and are not intended to change the processfrom reverse osmosis to forward osmosis. However, in an embodiment ofthe present invention, the process may be changed from RO to FO bychanging osmotic pressure reached via injecting of Additional Solution.This differs to a later embodiment wherein the process is changed fromRO to FO by permeate throttling until reaching a zero value of NDP (seebelow). With the injection of Additional Solution, the change in osmoticpressure may be significant (as example) 100 bar. The velocity ofosmotic pressure change can be very fast with no risk of membranedamage. The combination of providing a small gauge pressure change witha large osmotic pressure change allows one to reach concurrentlymembrane resonance oscillation by high frequency without risk ofmembrane damage with simultaneous backward flow, without the need to useexpensive high pressure permeate piping material.

Fouling carpet layer may be attached to membrane by adhesion and otherphysical forces. In order to effectively clean the membrane these forcesshould be overcome. Moreover, fouling, contrary to the membrane, istransparent to the gauge pressure, and under normal operation itexperiences no tensile stress and therefore it is not stretched. Inaddition, the fouling biofilm layer is characterized by low elasticityand a relatively short plastic deformation transition state before itbreaks and ruptures. Therefore, the two interconnected layers, theelastic membrane and the attached plastic biofilm, may be considered astwo connected membranes system each having different mechanicalfeatures. Moreover, the specific weight of the membrane is bigger thanthe specific weight of the biofilm. Differences in specific weightscauses result in different acceleration per pressure stroke. Thisdifferent response may contribute to the detachment and rupture processof the biofilm and the cleaning process of the membrane. It is anotheraspect of the present invention, to utilize these differences to enhancethe separation of the fouling biofilm carpet from membrane.

In order to detach the plastic biofilm fouling layer from an elastic ROmembrane the geometry of the elastic membrane has to be changed sharply.Such a change may be done by changing rapidly PGp or PGr by a waterpressure stroke. Since the plastic biofilm fouling layer is transparentto changes in gauge pressures, it will lag behind the elastic membrane.The plastic fouling biofilm layer will follow the elastic membranegeometry changes only due to the adhesion forces between them. Fast andfrequent geometry changes of the elastic membrane due to sagging anddisplacement caused by the water pressure stroke may create tensilestress between the two connected membranes along there connection areaand gradually open a gap between the elastic and the plastic membranesand will eventually detach them.

The pulsed water stroke may act as a hammer which directionally hits andmechanically shakes the membrane in a sequence of pulses characterizedas a wave of pressure surge. The pulse water stroke may be generated,for example, by a quick water's momentum change such as when flowingwater are forced to rapidly stop or start or change its direction offlow. A pulsed water stroke may occur when a valve is closed or openedquickly at the end of a pipeline system, and as a result a pressure wavepropagates along the pipe toward membrane module. Alternatively, thepulsed water stroke phenomenon may be initiated by a quick start or stopof a running pump delivering water into the line.

Pressure stroke waves can travel in and along the line as fast as thespeed of sound in the relevant water media and may reach all parts ofthe membrane module. A plurality or set of strokes may displace the freemembrane portions over the void spaces of the relevant spacer creatingtensile stress in and along the fouling biofilm, breaks it and detachesit from the membrane.

Quick alternation of gauge pressures PGp and/or PGr (pressure waves) mayprovide rapid and sharp membrane “shaking” resulting in an effectivemembrane cleaning.

Pressure waves may be generated selectively and separately on PGp and/orPGr. Selective generation of pressure waves over and on top of the gaugepressures of the permeate and/or feed may create a directional pressurestrokes across a free membrane portion having a feed-to-permeate orpermeate-to-feed directions respectively. The generator of the waterstrokes may be located in a distance from membranes and still beeffective. The Generator of the water strokes is preferably located inthe residual brine outlet or along the permeate inlet/outlet streams.Multiple water stroke generators may be connected to a single RO system.Multiple water stroke generators may be operated together, separatelyand/or in synch in order to create oscillations in feed-brine orpermeate gauge pressures.

In one embodiment, a water stroke generator is positioned along thepermeate and/or residual brine stream. Positioning a water strokegenerator along the permeate and/or residual brine stream is importantadvantage because of the distance from the feed pump which is sensitiveto pressure pulsation. There are thousands of displaceable free membraneportions between the feed pump and the water stroke generator, whichabsorb and damp the pressure pulsation before it reaches the feed pump.These free membrane portions accumulate energy in these elasticdeformation, when the valve on residual brine discharged is closed andgive it back when valve on residual brine discharged is open. Suchmechanism of kinetic and potential energy exchange, cannot work whenpressure pulse generation valve is positioned in the feed stream.

The water stroke generator may be configured to control the amplitudeand the frequency of strokes. Water stroke generator may be configuredto generate strokes in different frequencies, including frequenciesproportional to the natural vibration frequency of the membrane baseunit (The membrane base unit as used in this application refers to thebasic vibrating element described above which consists of a single voidspace covered by a free membrane portion). Water stroke generator may beconfigured to produce multiple frequencies. Multiple frequenciespressure waves may cause resonance effect in variety of basic unitsizes, enhancing biofilm fouling detachment effect.

The resonance point or area may be determinate by smooth tuning of thepressure pulsating frequency between 0.1 and 5 Hz for present on themarket membrane material. Novel membrane material such as zeolite,carbon, nanostructured, mix matrix that will come on the market may haveother resonance frequency. Resonance achievement is visible as an abruptincrease in turbidity of residual brine. The pulsating frequency has tohave variation in certain range as different parts of the membrane mayhave different resonance point. Simultaneous but different frequency maybe applied to PGp and PGr to reach abrupt increase in turbidity ofresidual brine. A single gauge pressure pulse may not able to causemembrane resonance oscillation. A set of a few tens of gauge pressurepulses may be required. In some heavy fouling application gauge pressurepulsation can be applied permanently, and additional solution appliedperiodically with intervals of few hours.

The process of pulsating FO backward flow may be provided by changingNet Positive Suction Head (NPSH) of osmotic pump. This effect may bereached by changing PGp water strokes in frequency from about 0.02 to0.1 Hz and amplitude about ±4 bar. Simultaneously via PGr water strokesmay be applied resonance membrane oscillation each one by differentfrequency and amplitude.

“Permeate Enclosure” comprises permeate channels, permeate tubes,pipelines and other equipment that are all in a fluid communication. Anysharp change in the amount of fluid within the enclosure, whetherincreasing or decreasing, will result in an increased or decreased ofits gauge pressure respectively and will generate a pulsed water stroke.The pulsed water strokes may provide several momentum changes in gaugepressures PGp and/or PGr based on different embodiments of the presentinvention. According to one embodiment, pulsed water stroke may begenerated by adding a pulse of excess permeate flow into the permeateenclosure from an external permeate source by a pump. Such a pulsedwater stroke may also be generated by a pulse wise increase-decrease ofout flow leaving the permeate enclosure using a generator of waterstroke.

Adding permeate flow, whether continuously or pulsed, from an externalsource through a pump into the permeate enclosure may be combined with asimultaneous subtraction of permeate out flow from the permeateenclosure. Such a permeate flow subtraction may also be in the form ofpulses provided by water stroke generator. Example of water strokegenerator may be Pressure Relief Valve (PRV) that includes plug andpressure adjustable spring. Such a combination of pump and PRV mayprovide two effects simultaneously. The first effect is that there willbe sufficient supply of permeate to PRV for pulse generation. Thisexcess in-flow supply, once suddenly stopped by the PRV, will generate ahalf-wave pressure increase. The second effect it that sufficient amountof permeate flow with required pressure will be supplied to the osmoticpump which generates the membrane backward flow.

Such an arrangement may be configured as known to the skilled man in theart to generate a directional-pulsed water stroke in a single frequencyor in a multiple of frequencies, randomly, independently orsynchronically.

Pulsed water stroke may also be generated by an ultrasound generatorsconfigured to deliver ultrasound waves onto and into elements of thepermeate enclosure. Pulsed water stroke may also be generated by anexternal piston moving in and out the permeate and/or residual brineline causing liquid volume changes in the line which in turns generatepressure water strokes. Pneumatic, hydro or electrical shock wavegenerators may also be used to generate such pulsed water strokes.Pulsed water stroke may be generated by and in many different forms asknown to the skilled man in the art.

Solution, which enters the feed channel and flows along the feed side ofthe membrane is termed herein as a “Raw Saline” (RS) solution. Solutionwhich leaves the feed channel of the membrane is termed herein as a“Residual Brine (RB)”. The RS solution which flows between the inlet andoutlet ports of the feed channel has an osmotic pressure POr and a gauge(hydrostatic or monomeric) pressure PGr.

Solution which flows on the permeate side of the membrane is termedherein as a “Permeate (PR)”. The PR has an osmotic pressure POp and agauge pressure PGp.

As thought by WO/2005/123232 termed “DOHS Process” Additional Solution(AS) with osmotic pressure POs>POr may be fed into the feed channel ofthe membrane for predetermined injection time. Such an injection willreverse the process across the membrane from a RO to a FO process andback to RO fast. In the same time on the same membrane and under thesame gauge pressure RO and FO processes may take place simultaneously onadjacent portions of the membrane as the AS pulse propagates downstream. This short AS injection, generates a short but strong permeatebackward flow across the membrane.

A balance of forces across a membrane portion will dictate whether itexperiences an FO or a RO process. Four forces are involved in thisbalance across a membrane portion from both the feed side and thepermeate side. This balance is called Net Driving Pressure (NDP). ThisNDP may further be termed as NDP-FO for a Forward Osmosis process orNDP-RO for a Reverse Osmosis process.NDP (FO or RO)=PGr−POr−PGp+POp. where:

POr and PGr are the osmotic and gauge pressures of the RS solution, andPOp and PGp are the osmotic and gauge pressures of the PR solution.

If the balance of these four forces across a specific membrane portionis positive (+) the process is called Reverse Osmosis NDP-RO and PR issqueezed out from RS solution via the semi-permeable membrane.

If the balance of these four pressures across a specific membraneportion is negative (−) the process called Forward Osmosis NDP-FO and PRis sucked into the RS solution via the semi-permeable membrane.Injection of AS instead of RS may switch the osmotic process across themembrane from a RO to an FO or vice versa, depending on the new balanceof the net driving pressure, that will be reached with this ASinjection. According to one aspect of the present invention, injectingthe AS may be done as a full replacement of the entire RS flow or bymixing AS and RS together before their entrance into the feed channel.The effective osmotic pressure of the AS or the mix of the AS with theRS dictates the osmotic pressure POs on the feed side of the membrane.

The practical implementation of an FO process shows that sagging doesnot take place due to sharp changes in osmotic pressure. Osmoticpressure applies only to water molecules and cannot change membrane'sgeometry. Sharp change of an osmotic pressure may change the directionof flow from a RO to an FO, but is incapable to change membrane shapeand cannot cause membrane delamination and damage. It is absolutely safefor membrane integrity to undergo momentarily high amplitude change ofosmotic pressure, in contrast to rapid and high amplitude change ofgauge pressure that may cause membrane distraction.

According to one embodiment of the invention, combining FO backward flowand pulsed water stroke that mechanically shake the membrane at the sametime instant, provides a synergetic result which improves foulingremoval effectiveness. There are several possibilities to practice it.Two of these possibilities will be discussed herein as non-limitingexamples.

According to one embodiment of the present invention, synchronizingpulsations of FO backward flow and pulsed water stroke (mechanicalmembrane shaking) may have an additional benefit over continues FObackward flow and pulsed water stroke. In such a pulsating FO backwardflow regime smaller volume of permeate crosses the membrane. Therefore,the AS pulse is less diluted during its propagation downstream along themembrane. To say it in other words, the higher and the longer durationthe AS concentration lasts, the stronger the negative driving pressure,the stronger the backward flow and the cleaning effect. In addition,keeping the AS concentration less diluted enables using lower initial ASosmotic pressure POs or shortening its injection time while keeping thesame cleaning effect. According to one aspect of the present invention,sacrificing permeate as backward flow for cleaning purposes, should bemade simultaneously with a pulsed water stroke causing free membranemechanical shaking toward the same direction. Time and directionalsynchronization between permeate backward flow and mechanical membraneshaking will enhance the effect of fouling separation and may consumeless AS and less permeate. The membrane cleaning process according tothis embodiment of the invention is based on mechanical forces ratherthan chemicals. As such, it is another aspect of the invention to offeran environmentally friendly solution.

In an alternative embodiment of the present invention, mechanicalshaking of the free membrane portions to detach foulant is again carriedout by applying, for a predetermined period of time, a plurality ofdirectional pressure strokes PGp and/or PGr on the permeate and/orresidual brine membrane side. In addition, a pulse-wise flow regime isapplied in the residual brine stream to increase the shearing force tothe membrane thereby achieving enhanced fouling evacuation. In thisembodiment, no additional solution is required and the process may becarried out during the normal RO procedure.

In this embodiment, the pressure strokes are precisely synchronized withflow pulsation. Precise synchronization is applied between peaks ofpressure strokes and peaks of pulse-wise flows in separation module,thereby achieving simultaneous enhanced flip foulant up and itsevacuation by increasing shearing force. The generator for purpose ofprecise synchronization of gauge pressures strokes and/or flow pulse,comprises piston or other similar means such as diaphragm, each side ofwhich, is in flow communication with separation module inputs and/oroutlets synchronization of which is requested.

As a non-limiting preferable example, precise synchronization may beapplied in the following alternating sequence: PGr pressure decreasing,shearing force increasing; PGp increasing; followed by PGr pressureincreasing, shearing force decreasing, PGp pressure decreasing, therebyproviding synergetic enhancement of fouling detachment and evacuation.The required cleaning effect is achieved when the free membrane portionsshaking provided by residual brine gauge pressure PGr sharp decrease isprecisely synchronized with permeate gauge pressure PGp sharp increaseand precisely synchronized with residual brine flow velocity increase.This may be achieved by connecting the water generator to a 3-way valveconnected to the residual brine stream, permeate stream and to drain.The 3-way valve may switch the water stroke generator between twopositions to provide the required sequence, as follows:

Position 1: The 3-way valve opens brine flow to water stroke generatorcausing PGr decrease, shearing force increase and permeate pressure PGpincrease; and

Position 2: The 3-way valve closes brine flow and connects water strokegenerator to drain, causing PGr increase, shearing force decrease andPGp decrease.

In this aspect of the present invention an additional cleaning activitymay be carried out an intervals comprising a periodic osmotic backwash(POB) which may be performed with or without oxidation.

The periodic osmotic backwash is based on high frequency (several timesa minute) changes from Reverse Osmosis (RO) to Forward Osmosis (FO).This is brought about without feeding of Additional Solution to the feedside of the membrane but rather involves reaching neutral value of NDPby glide changing PGp and/or PGr combined with extremely fast andprecise synchronized changes of the residual brine and permeate gaugepressures; decrease PGr, increase PGp and vice versa. In this respect,the process changes from RO to FO when the sign of net driving pressure,defined by the balance of osmotic and gauge pressures PGr, Por, Pop andPGp, changes. Glide changing PGp and/or PGr until neutral value of NDPmay be done in several ways by throttling permeate outlet, feed flowinput, residual brine outlet or some of them. Preferable option isthrottling permeate outlet as this is the simplest from a practicalpoint of view.

In an alternative embodiment, the quick back and forth movement ofpermeate across the membrane caused by changing the process between ROand FO as described above is enhanced by the inclusion of a strongoxidizing agent. This involves the additional step of injecting cleaningsolution into the permeate enclosure, preferably before the permeatethrottling step.

First Example: Continuous FO Backward Flow and Pulsed Water Stroke(Mechanical Membrane Shaking)

A combined, continuous FO backward flow and pulsed water stroke methodfor cleaning a semi-permeable membrane in a reverse osmosis separationmodule may be made in the following way. A membrane has a feed and apermeate side facing a feed channel and a permeate channel respectively.Foulant is mainly located on the feed side. The membrane normallyperforms Reverse Osmotic Process producing desalinated water (permeate).A RO process may take place in the following way: feeding a salinesolution under gauge pressure PGr and an osmotic pressure POr, removingresidual brine from the membrane feed side. Permeate having gaugepressure PGp and osmotic pressure POp penetrates from feed side topermeate side accordingly to net driving pressure defined by the balanceof the pressures PGr, POr, Pop and PGp.

A membrane cleaning session is conducted in the following way: Feedingthe feed side of a membrane, for a predetermined injection time,Additional Solution having an osmotic pressure POs>POr chosen in such away that the net driving pressure becomes opposite to the normaloperation, whereby a backward flow of permeate is induced, so as to liftand remove foulant. At the same time, a set of pulsed water strokes isapplied to cause a mechanical membrane shaking, so as to enhance thelift and removal of said foulant by superposition of hydraulic andmechanical forces. Such set of water strokes may be provided by a waterstroke generator positioned in residual brine stream and/or permeatestream.

Second Example: Synchronization Between Pulsating FO Backward Flow andPulsed Water Stroke (Mechanical Membrane Shaking)

This phenomenon of strong permeate flow pulsation during osmoticbackward flow, is related to a Net Positive Suction Head (NPSH) of anosmotic pump. According to one aspect of this embodiment, in order totake greater advantage of the osmotic backward flow, it has to work in apulsed flow regime, synchronically with the mechanical membrane shakingcaused by the pulsed water stroke. An osmotic pump is NPSH dependent,similar to a conventional centrifugal pump. The “required NPSH value”for a centrifugal and osmotic pump is defined as the minimal suctionpressure, below of which the pump is unable to deliver expected floweven if the motor rotates in full power.

The NPSH value for osmotic pump is PGp. There is a minimum permeatepressure PGp, the “required NPSH value”, below of which osmotic pump isunable to deliver flow even if the osmotic pressure of AdditionalSolution POs across the membrane is very high. The semi-permeablemembrane layer acts, in this regard, as the impeller of an osmotic pump.

This PGp is a function of the hydraulic pressure losses in commonpermeate piping, central permeate tubes, and tight permeate channels.The membrane support layers themselves also contribute to some permeatepressure losses.

If PGp is above “required NPSH value”, the osmotic pump able to pushesflow of permeate proportional to NDP-FO. If PGp is below “required NPSHvalue”, the osmotic pump is unable to deliver permeate flow. In the textbelow we will use the term “NPSH” instead of “required Net PositiveSuction Head value”.

According to another embodiment of the present invention, the pulsedpermeate water stroke may provide PGp pressure fluctuations below andabove the NPSH. In such way, the pulsed pressure water stroke becomesthe triggering switch which enables the alteration of the osmotic pumpflow. Since osmotic pumps do not have massive inertial parts, their flowchanges from a minimum to a maximum flow take place immediately.

This combination of mechanical membrane shaking and permeate backwardflow pulse of osmotic pump may be synchronized in time and direction.

Pulses of permeate backward flow may be applied exactly in thesemilliseconds when membrane is in its maximum amplitude of shaking. Anygap occurs due to such shaking between the membrane and the fouling, maybe filled by the permeate flow. Such permeate penetration between themembrane and the fouling, further decreases the adhesion forces existingbetween membrane and the fouling and further causing fouling carpetrupture and detachment.

Experimentally it was found that for brackish spiral RO membrane thatare presently on the market, the NPSH during Forward Osmotic & WaterStroke (FO&WS) cleaning can be reached when permeate pressure PGp incommon permeate pipe line is about 3 bar gauge. To provide pulses ofpermeate backward flow during forward osmosis process the PGp may bechanged from vacuum value (−1) to 7 bar, in other words it is ±4 baramplitude. For other types of membrane this value has to be foundexperimentally as the pressure which provides the most effectivecleaning. For new carbon and nanoparticles membranes which may becommercially available soon, it is expected that their NPSH will bediminished due to lower hydraulic loss associated with permeate movementvia membrane. Significant hydraulic losses are associated however, withhydrophobic feathers of their support layer. Treatment of such membranesby a Polydopamine or similar solutions which makes the membrane'ssupport layers hydrophilic may further increase the effectiveness of thecleaning methods thought by this invention, or diminish the amount of ASrequired. Alternatively, adding Polydopamine or a similar solution whichmakes the support layer of such membranes more hydrophilic before orduring the Additional Solution may increase the effectiveness of thepresent invention. Such a solution may be for example alcohol. Alcoholor a similar solution may be added before or during the injection of AS.Alternatively, it can be added into the feed line in a RO processes orinto the permeate line in an FO processes. This technology is expectedto be most effective in the food processing, pharmaceutical andsemiconductors industry.

Additional aspects of this invention may increase the membrane cleaningeffect by increasing osmotic coefficient or activity coefficient of theadditional solution. As known to the skilled man in the art, thatosmotic pressure depends on the activity coefficient and the activitycoefficient is related to the diffusion coefficient. Therefore, thehigher the activity and the diffusion coefficients the higher theosmotic pressure of the same solution concentration.

According to another embodiment of the present invention, water may betreated by a magnetic, an electromagnetic or a microwave filed in orderto reduce the size of water clusters and break the hydrogen bondsstructure of the water molecules in the aqueous electrolyte solution.

Water mixed with dry salt for the on-site preparation of the additionalsolution, may be magnetically treated to have an increased osmotic,diffusion and activity coefficients, due to the water smaller clusters,reaching higher osmotic pressure POs value. According to another aspectof the present invention, a permanent magnet may be positioned in thewater tank where dry salt dissolving process takes place. According tothis embodiment, the solution has to circulate under the magnetictreatment field several times during the dissolving process in order toachieve an effective water clusters break. Therefore, according toanother embodiment of the present invention the Additional Solution maybe circulated under the influence of such a magnetic field just beforethe time in which it is injected into the feed channel.

According to another embodiment of the present invention, AdditionalSolution is actually Draw Solution implemented in FO and PRO processes.A magnetic treatment, as mentioned above, of this Draw Solution mayincrease its activity coefficient and therefore its actual effectivenessby an increased osmotic pressure.

This increase in actual effective osmotic pressure of the AS isecologically important because less AS solution may be required for thesame effectiveness level of membrane cleaning.

The self-diffusion coefficients of the Na+ and Cl− ions in 5M (mole)concentration (Additional Solution based on NaCl), may be increased byan about 17% to 25% as the magnetic field strength increases from 0.5Tesla to 2 Tesla.

The present invention may impact the entire scheme of water treatmentand may allow the production of higher water purity.

According to one embodiment of the present invention, it may allowavoiding the commonly used practice of chlorination e.g. chloramine, ina pretreatment process in a RO module. The absence of chlorinationpretreatment prevents the formation of chlorination by-products such astrihalomethanes and the risk of semipermeable membrane oxidation.Current RO modules are unable to reject small size organic moleculessuch as, for example, pharmaceutical, pesticides or hormones. TOCmeasurements done on the permeate products of existing RO systems detectabout 100 ppb of such organic matter which passes the RO membranes.Removal of this organic material in the presence of chlorinationby-products is less effective. By avoiding such by-product, as thecurrent invention allows, enables effective implementation of ultrafiltration (UF) module positioned downstream of the semipermeablemembrane in a configuration which is known to the skilled man in the artfor conduction batch absorption. UF module installed on the permeateside, downstream the RO module may be available to capture this organicmaterial. Activated carbon is one non-limiting example for a sorbentthat may be used in an UF as batch or online absorber. Sorbent may bedosed into the feed stream of a UF module in the beginning or during ofeach filtration cycle. UF module act as an absorber vessel in whichexternal mass transfer and surface diffusion take place between sorbentand organic material.

Third Example: Precise Synchronization Between Pulsed Water Stroke(Mechanical Free Membrane Parts Shaking) with Flow Pulsation

In yet another aspect of the present invention mechanical shaking of thefree membrane portions to detach foulant is again carried out byapplying, for a predetermined period of time, a plurality of directionalpressure strokes PGp and/or PGr on the permeate and/or residual brinemembrane side. In addition, a pulse-wise flow regime is applied in theresidual brine stream to increase the shearing force to the membranethereby achieving enhanced fouling evacuation. In this embodiment, noadditional solution is required and the process may be carried outduring the normal RO procedure.

In this embodiment, the pressure strokes are precisely synchronized withflow pulsation, preferably in the alternating sequence: PGr pressuredecreasing, shearing force increasing; PGp increasing; followed by PGrpressure increasing, shearing force decreasing, PGp pressure decreasing,thereby providing synergetic enhancement of fouling detachment andevacuation. The required cleaning effect is achieved when the freemembrane portions shaking provided by residual brine gauge pressure PGrsharp decrease is precisely synchronized with permeate gauge pressurePGp sharp increase and precisely synchronized with residual brine flowvelocity increase. This may be achieved by connecting the water strokegenerator to a 3-way valve connected to the residual brine stream,permeate stream and to drain. The 3-way valve may switch the waterstroke generator between two positions to provide the required sequence,as follows:

Position 1: The 3-way valve opens brine flow to water stroke generatorcausing PGr decrease, shearing force increase and permeate pressure PGpincrease; and

Position 2: The 3-way valve closes brine flow and connects water strokegenerator to drain, causing PGr increase, shearing force decrease andPGp decrease.

Fourth Example: Precise Synchronization Between Pulsed Water Stroke(Mechanical Free Membrane Parts Shaking) with Flow Pulsation andPulsating Osmotic Backwash RO-FO-RO (with or without Oxidation)

In this aspect of the present invention discussed in the fourth examplean additional cleaning activity may be carried out an intervalscomprising a periodic osmotic backwash (POB) which may be performed withor without oxidation. This activity is made on-line without stopping thefeed pump, with very limited interruption in the normal desalinationprocess.

The periodic osmotic backwash is based on high frequency (several timesa minute) changes from Reverse Osmosis (RO) to Forward Osmosis (FO).This is brought about without feeding of Additional Solution to the feedside of the membrane but rather involves extremely fast and precisesynchronized changes of the residual brine and permeate gauge pressures;decrease PGr, increase PGp and vice versa. In this respect, the processchanges from RO to FO when the sign of net driving pressure, defined bythe balance of osmotic and gauge pressures PGr, Por, Pop and PGp,changes.

Thus, the periodic backwash procedure (POB) adds an additional step ofthrottling permeate exiting from permeate enclosure, increasing permeategauge pressure PGp until the NDP value become equal to zero. Innon-limiting numerical example, PGp increases from 1 bar to 9.1 bar.NDP (Neutral)=+12−3−9.1+0.1=0.0 bar

Precisely synchronized directional strokes with oppose directed changeof pressure: PGp (between 11.5 and 12.5 bar and PGr (between 9.6 and 8.6bar) providing plurality of quick RO-FO-RO process changes.NDP (FO)=+11.5−3−9.6+0.1=−1.0 bar. Sign (−) means the process is FONDP (RO)=+12.5−3−8.6+0.1=+1.0 bar. Sign (+) means the process is RO

In an alternative embodiment, the quick back and forth movement ofpermeate across the membrane caused by changing the process between ROand FO as described above is enhanced by the inclusion of a strongoxidizing agent. This involves the additional step of injecting cleaningsolution into the permeate enclosure, preferably before the permeatethrottling step. PO&OB may be implemented for membranes such asgraphene, zeolite, carbon, ceramic, nanostructured, mix matrix etc. thatare able to withstand a high concentration of strong oxidizers.

In this embodiment, a preferred sequence of steps is as follows:

Step 1: Cleaning solution injected in one side of permeate enclosure andfill it up, when separation module is in normal RO operation.

Step 2: Throttling permeate exiting from permeate enclosure. ReachingNDP (Neutral).

Step 3: The 3-way valve in Position-1 opens brine flow to water strokegenerator, causing: PGr decreasing; PGp Increase. Process changed fromReverse Osmosis to Forward osmosis. Backwash by permeate takes place andfouling evacuation by high shearing force. (Fouling oxidizes ordissolves option PO&OB).

Step 4: The 3-way valve in Position-2 closes brine flow and connectswater stroke generator to drain. PGr increasing due to water hammercaused by sudden valve closing; permeate pressure PGp decreasing, causedby sudden opening brine side of water stroke generator to drain;Shearing force in feed membrane side decreasing. Process changed fromForward osmosis to Reverse Osmosis. Permeate goes back to permeate area.In PO&OB option chemical solution filtrate itself by this back movementvia membrane.

Steps 3 and 4 are repeated frequently causing “back and forth” dozens oftimes backwash and, optionally, dozens of fouling oxidation, or scalingdissolution.

Step 5: Cleaning solution moves back to storage tank forre-concentration and reuse.

Step 6: Permeate enclosure opens by valve and begin normal RO operation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1, 1 b and 1 c are schematic and expanded views of an RO systemaccording to an embodiment of the present invention;

FIG. 2 is a graph illustrating an alternating permeate PGp pressurebelow and above NPSH by pump 10;

FIG. 3 is a graph illustrating alternating permeate PGp pressure by pump10 and PRV 13;

FIG. 4 is a Flow and pressure graph for selection permeate pump 10 andPRV 13;

FIG. 5 is a schematic drawing illustrating the present inventionincorporated into the entire scheme of water treatment;

FIG. 6 is a general view of a membrane module incorporated into anarrangement for AS preparation and injection;

FIG. 7 is a graph showing “Amplitude-Frequency” area; and

FIG. 8 is a schematic view of a system according to another embodimentof the present invention having a water stroke generator for pressureand flow pulsation.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 1 is a schematic view of a RO unit comprising a reverse osmosis(RO) separation module 100. Tank 20 contains Raw Saline solution (RS)21. Tank 23 contains additional solution 24. Feed pump 22 pumps rawsaline solution into a feed channel 5 and toward a membrane feed side 8.Raw saline solution which comprises a solvent and dissolved salts, movesalong the membrane feed side 8 under gauge pressure PGr and has anosmotic pressure POr. Residual brine is removed via outlet (RB) 28.

Semi-permeate membrane 14 has a feed side 8 and a permeate side 15. Feedspacer 6 maintains a gap between two opposing feed sides 8 of twoopposing membranes 14 and defines the feed channel 5. During a ROseparation process, permeate (PR) 27 has an osmotic pressure POp and agauge pressure PGp, and is driven by a positive net driving pressuredefined by the balance of the four pressures PGr, POr, POp and PGp, andpenetrates via membrane 14 into the permeate channel 4 which is shown indetail in FIG. 1 c.

Basic unit 300 in FIG. 1c is defined by a pair of adjacent solidpermeate spacer ribs 7 which maintain gap 4 between two opposingpermeate sides 15 of two opposing free membrane portions 16 of membrane14. As mentioned above, membrane 14 tends to get a wave-like geometrydue to a higher PGr than PGp and due to the mechanical support providedby the grid of the rigid ribs of the permeate spacer 7.

A typical spiral membrane element may have an about 40,000 basic units.A basic unit 300 may have a dimension of an about 0.5 mm in width and1,000 mm in length. A drumhead of a stretched membrane over a void space4 of the permeate channel consists of stretched free membrane portion 16located between two opposing solid fibers of permeate spacer 7.According to the present invention, periodic oscillations of thepressure difference between PGr and PGp, cause an oscillatingdisplacements of free membrane portions 16.

As shown in FIG. 1b and FIG. 1c , membrane 14 and free membrane elements16 may be displaced from a first position 80 to a second position 80′.It is one aspect of the present invention, to induce such displacementsby changing the ratio between PGr and PGp temporarily, in a synchronizedway or in an unsynchronized way, in a way which may cause a quick pulseddisplacement characterized by a certain direction. Such a direction ispreferably from the permeate channel toward the feed channel.

Due to the wave-like geometry of membrane 14, as mentioned above, flowof the raw solution in the feed channel experiences velocity changes.The feed flow velocity tends to be higher in narrow spaces in feedchannel 5, such as the spaces above the solid ribs 7 of the permeatespacer which gives no room to membrane 14 to bend (sag) toward thepermeate channel. These areas are characterized as supported membraneportions 18 which has no room to bend (sag) toward the permeate side.The feed flow velocity tends to be lower in wider spaces of the feedchannel 5, such as in the feed channel spaces located above voidpermeate channels spaces 4 which has no rigid support. Such places arecharacterized by free membrane portions 16 which have room to bedisplaced and bend (sag) toward the permeate side and toward the feedside, as a function of the ratio and/or changes of this ratio, of thePGr and PGp. Moreover, due to these changes of feed flow velocity, anddue to other factors, in general fouling 9 tends to be thicker abovefree membrane portions 16 and thinner above supported membrane portions18.

As shown in FIG. 1b , feed spacer 6 and permeate spacer 7 maintain gapsbetween opposing membranes. Gap 5 between two opposing feed sides 8 oftwo opposing membranes 14, in which feed spacer 6 is located, is definedas the feed channel 5 and it is in a fluid communication with feed pump22 and residual brine outlet 28. Gap 4, which is located between twoopposing permeate sides 15 of two opposing membranes 14, in whichpermeate spacer 7 is located, is defined as the permeate channel and itis in a fluid communication with permeate pipe 29.

As shown in FIG. 1, permeate channel 4 is in fluid communication withtank 26 contains permeate 27 through valve 12, and pipeline 31 withpressure relief valve 13 and pump 10 with valve 11. An arrangement, forexample, such as pump 10, valve 11 and a pressure relief valve 13 may beconfigured to create a pulsed water stroke of an increased PGp pressure.

Other arrangements may include pressure relive valve 109 that takes allor part of the residual brine stream via line 128 from pipeline 28 anddischarge it via pipeline 129. Pressure relive valve 109 may beconfigured to create a pulsed water stroke in different frequencies,smoothly change frequency, and adjust water stroke frequency to membranenatural frequency, and reach membrane resonance oscillation. Suchpressure relief valve or water stroke generator may be controlled byspring, diaphragm, solenoid or other means. It can be adjusted manuallyor automatically. In multi stage RO systems the pressure relief valvemay be installed in interstate residual brine stream.

FIGS. 2 and 3 illustrate changes in PGp and PGr pressure during cleaningprocess FO&WS and have to be considered together with FIG. 1. FIGS. 2and 3 show a smooth sinusoidal waveform, including half-wave increaseand half-wave decrease, of gauge pressures and also illustrate sequencesin which different devices are activated.

Process Description

The present invention covers a variety of options for membranemechanical shaking without, but preferably with resonance, by means ofPGp and/or PGr gauge pressure strokes, optionally combined withreversing osmotic processes from RO to FO or opposite, by means ofinjecting additional solution that changes the osmotic pressure from POrto POs that starts an osmotic pump. The osmotic pump may providecontinuous backward permeate flow or more preferably, in pulsation formfollowing NPSH PGp pressure. Due to wide variety of options, only a fewprocess examples will be described below and with reference to theaccompanying drawings.

In accordance with one embodiment of the invention, during a RO process,a cleaning procedure consisting of FO&WS can be initiated by closingvalve 12, starting pump 10 which pumps permeate 27 from tank 26 intopermeate channel 4 via pipeline 30 and 29. The beginning of cleaningprocedure may be seen as timeline 77 on FIG. 2. Pulse water strokes maybe generated by series of quickly opening and closing valve 11 whichmove free membrane portions 16 of a basic unit 300 displacement(shaking) from a position 80 to a position 80′. Continuation of openingand closing valve 11 that causes set of pulse water strokes by frequencyin the range about 0.02 to 0.1 Hz, by amplitude about ±4 bar, duringcleaning procedure is presented on FIG. 2 as PGp smooth sinusoidalpulsation line 76. Note that this PGp pressure stroke has no possibilityof, and is not intended to change NDP balance from RO to FO, but only tomechanically shake membrane. Finishing point of cleaning procedure takesplace when pump 10 stops, valve 11 is closed, valve 12 is opened and theseparation module 100 continues its normal RO separation process, as maybe seen as timeline 82 on FIG. 2. The actual time passing betweentimelines 77 and 82 is about three to five minutes. Fouling 9 which islocated on membrane 14 may experience mechanical pulsed directionaldisplacement force 1 that causes its detachment from membrane 14 and itsremoval with residual brine 28.

In accordance with one embodiment of the invention, at the same timeline77 on FIG. 2, instantaneously with pulse water stroke described above, apulse of additional solution 24 from tank 23 may be fed into pump 22instead of the raw solution 21 coming from tank 20 or in a combinationwith it. This may be done by opening valve 25 for about 3-50 seconds.The AS injection switches the osmotic pressure on the feed side 8 ofmembrane 14 from POr to POs. As a result, the new balance of the netdriving pressure across membrane 14 experiencing the AS pulse,temporarily reverses the process from RO to FO and backward flow 2 ofpermeate 27 toward feed channel 5 takes place.

Fouling 9 which is located on membrane 14 may experience three forces: afirst force 1, which may be generated due to a mechanical membranepulsed directional displacement (shake) as a result of the pulsed waterstroke; a second force 2, which may be generated by a permeate backwardflow due to a temporarily backward permeate flow across membrane 14caused by a pulse of an AS; and a third shearing force 3, due to thelongitudinal feed and residual brine flow in the feed channel. Thisthird shearing force 3 may increase during such a pulsed water strokedue to a simultaneous increased velocity of the feed flow. Such asimultaneous velocity increase may happen due to the following reasons:(a) The feed flow may increase due to fact that permeate is not squeezedout of the feed channel at that time into the permeate channel ratherthan the opposite, permeate flows backward from the permeate side intothe feed side and increasing its flow; (b) The cross section of the feedchannel 5, at least in the relevant area which experiences the pulsedwater stroke, becomes narrower due to the fact that free membraneportions 16 are displaced toward the feed channel from a first position80 to a second position 80′. The superposition of the above factors andforces act together to enhance the detachment of fouling 9 from membrane14 and removal with residual brine.

According to an alternative embodiment of the invention, permeatebackward flow 2 may take place not continuously as explained above, butonly in the microseconds when membrane mechanical shaking 1 is in itsmaximum amplitude. This synchronization may take place when PGpfluctuation, line 76, cross about in the middle of the line 83 that maybe equal to NPSH value of osmotic pump (FIG. 2).

When PGp pressure is above NPSH value 83 the FO process providesbackward permeate flow proportional to NDP-FO, when PGp pressure isbelow NPSH value 83 FO process cannot provide backward permeate flowproportional to NDP-FO, lines 76 and 83 (FIG. 2). Therefore, theaccumulative effect is: a pulse of mechanical shaking and a pulse ofbackward permeate flow for fouling separation which may be stronger thana pulse of mechanical shaking and a continuous backward permeate flow.

Pulsating permeate backward flow 2 during FO&WH cleaning process has anadditional benefit over continuous forward osmotic backward flow 2. Inthe pulsating form, a smaller amount of permeate crosses the membrane.Since permeate which crosses the membrane into the feed channel dilutesthe additional solution 24, a smaller amount of permeate which crossesthe membrane the lower the dilution and the concentration of theadditional solution 24 lasts longer and may still be effective towardthe end of the FO&WH cleaning process. Alternatively, due to the lowereddilution effect, it may be possible to use an additional solution havinga lower osmotic pressure POs or generating shorter injection pulses ofan additional solution in order to get the same cleaning effect.

Pulsating PGp to provide backward permeate flow 2 may be made in“Amplitude-Frequency” area “A” shown on FIG. 7. The frequency is about0.02 to 0.1 Hz and amplitude up to ±4 bar measured on the feed end ofpressure vessel. The upper limit of the gauge pressure change velocity,10 psi per second, should not be exceeded. This limiting value 10 psiper second is shown as line 500 on FIG. 7.

As mentioned above, the cleaning process based on this invention isecologically friendly because it is based on mechanical energy ratherthan chemicals.

Additional embodiments of this invention may increase the membranecleaning effect by creating membrane oscillation by gauge pressurestrokes PGp shown on FIG. 1b as arrowhead 1, having a frequencyapproximately equal to natural frequency of about 2.5 Hz of the freemembrane portions 16 in order to get a resonance and enhanceddisplacement. Membranes oscillating in a frequency proportional to theirnatural frequency may increase the amplitude of their vibration(resonance effect). Opening and closing valve 11 cannot be made at 2.5Hz frequency. Water Stroke Generator such as Pressure relief valve (PRV)13 may be implemented to provide such frequent oscillation of PGp.

In accordance with one embodiment of the invention, during a RO process,a cleaning procedure FO&WS can be initiated by closing valve 12,starting pump 10 and keeping valve 11 continuously open. Pump 10 pumpspermeate 27 from tank 26 into permeate channel 4 via pipeline 29, 30, 31and via PRV 13 discharging it to tank 26 as a pulse flow. The beginningof cleaning procedure may be seen as timeline 86 on FIG. 3.

The configuration of PRV 13 may be selected by the ability to dischargepermeate 27 as a series of pulses and create flow-induced vibrations.

Pulse water strokes generated by PRV 13 motivate free membrane portions16 of a basic unit 300 resonance displacement (shaking) from a position80 to a position 80′, frequency about 2.5 Hz. Continuation of PRVflow-induced vibrations cause pulse water stroke during cleaningprocedure shown on FIG. 3 as smooth, sinusoidal PGp pulsation line 92around certain pressure 116. Free membrane portions 16 resonanceoscillation for different membrane types may be in range of frequency0.1 to 5 Hz with best results reached with 2.5 Hz for certain membranetypes. The amplitude in this frequency range should be low and notexceed ±3 bar measured on feed end of pressure vessel. This recommendedarea of membrane resonance is marked as area “B” on FIG. 7. This PGppressure stroke has no possibility or intention of changing NDP balancefrom RO to FO, but only provides for membrane resonance shaking. Thefinishing point of the cleaning procedure takes place when pump 10stops, valve 11 is closed and valve 12 is opened, with the separationmodule 100 continues its normal RO separation process as may be seen astimeline 89 on FIG. 3. The actual time passes between timeline 86 and 89is about three to five minutes. Fouling 9 which is located on membrane14 may experience mechanical pulsed directional displacement force thatcauses its detachment from membrane 14 and its removal with residualbrine 28.

In accordance with one embodiment of the invention at the same timeline86 on FIG. 3, instantaneously with the pulse water stroke describedabove, a pulse of additional solution 24 from tank 23 may be fed intopump 22 instead of the raw solution 21 coming from tank 20 or in acombination with it.

FIG. 4 of the accompanying drawings shows an example of selectionpermeate pump 10 and pressure relief valve 13 by flow and pressureaccording to one embodiment of the present invention. Such arelationship may demonstrate, at least in one way among possible otherways, how to define pump 10 characterized by a curve 71. FIG. 4 furthershows some aspects related to the requirements of pressure relief valve13 according to this one embodiment.

In general, the flow output of permeate pump 10 and PRV 13 may beselected to meet the RO module nominal permeate production rate which isdefined in FIG. 4 as point “A”. The pressure output of permeate pump 10,at its shut-off point 70, may be selected so that it is about 20% belowthe pressure rate of permeate pipe 29. Because of implementation smallPGp amplitude, the present invention allows the use of low-pressureplastic permeate lines. Permeate pump 10 may have a flat pressure-flowcharacteristic. Permeate pump 10 may be equipped with a VSD to simplifythe adjustment between pump duty pressure and the PRV's pressure setpoint “A”.

Pressure relief valve or other water stroke generator 13 may be selectedto meet the nominal permeate out flow 73 of RO module 100, and pressurerelief set point “A”. Above this point “A” PRV relieves permeate flow 27at frequency between 0.1 and 5 Hz. The frequency of such pressurepulsations may be smoothly adjusted, for example, by adjusting springtension or changing water passes to diaphragm valve or by PROGRAMMABLELOGIC CONTROLLER changing the frequency automatically or manually untilhighest turbidity of reject brine flow will be reached. An increase inturbidity indicates that resonance was reached. It is recommended tomake variations of frequency near by or close to the best frequency.

Pumps 10 and 22 should hydraulically and/or electrically communicate inorder to control and stop pump 10 immediately if pump 22 has stopped forany reason. This safety precaution has to be duplicated and eventriplicated to ensure that permeate pressure PGp will never be more thanthe feed pressure PGr as known to the skilled man in the art.

In accordance with one embodiment of the invention, membrane oscillationcan be initiated by pulse water strokes PGr generated by PRV 109positioned in residual brine stream 28. The pulse water strokes PGr mayhave sinusoidal pulsation 93 around nominal PGr pressure 116. Thepressure presented as line 116 on FIG. 3 may have very different valuefor PGp and PGr pulsation.

Membrane mechanical shaking 1 may be made by gauge pressure stroke PGrand/or PGp in “Amplitude-Frequency” range “B” shown on FIG. 7. Thefrequency is in range of about 0.1 to 5 Hz. It is recommended not toexceed gauge pressure amplitude more than ±3 bar, measured on commonmanifold at the feed end of pressure vessels. It is recommended not toexceed the 45 psi/second oscillation velocity, line 501 on FIG. 7.

For seawater applications, it is recommended to apply PGr gauge pressurestroke amplitude below ±5% of the normal operation range. To beeffective, PGr pulsation has to be smooth sinusoidal, the water strokesgenerator has to have smoothly adjustable frequency. As described above,an indication of resonance is demonstrated by an increase in turbidityof the residual brine stream.

FIG. 5 of the accompanying drawings shows a standard UF module operatingas Ultra-Filtration Batch Absorber 110 positioned down stream of ROmodule 100 and receives permeate 29 as feed. Sorbent injects via dosingsystem 115 continuously or as a pulse in to UF module 110, at the rateaccording to required water quality. Sorbent accumulates in UF moduleduring dead-end filter cycle, and performs mass transfer and diffusionwith organic matter presented in permeate stream 29. Dead-end filtrationcycle keeps sorbent in UF fibers until it sorption capacity isexhausted. During periodic backwash, sorbent 115 may be discharged viaoutlet 112. The high purity product without organic matter is deliveredfrom outlet 113.

FIG. 6 shows a general view of membrane module and arrangement foroptions of additional solution preparation and injection.

Raw saline solution 21 passes through micronics filter 50. Feed Pump 22pumps raw saline solution 21 into the RO module 100. Product leavesmodule 100 via pipeline 29, residual brine is removed via pipeline 28.According to one embodiment of the invention, additional solution 24 maybe fed into the membrane from a syringe type pump 51. This syringe pumpmay have a vertical arrangement of pipes. The syringe pump may becharged from the bottom by an additional solution 24 from tank 52 and bya pump 53 via filter 54. Syringe pump 51 operates by pressure drop onmicronics filter 50. No piston is needed in the syringe pump, becausedifference in specific gravity between the raw saline solution 21 andthe additional solution 24 is enough to prevent a mix of the two.Additional solution 24 may be prepared from a residual brine removed viapipeline 28 during previous FO&WS cleaning procedure. Additionalsolution 24 does not chemically interact with the fouling. The aim ofthe additional solution is only to serve as an osmotic source of energyto operate the forward osmotic pump during a FO&WS cleaning. Theconcentration of the additional solution may be diminished due todilution by permeate backward flow during cleaning, however itsconcentration at the end of the process is still quite high, and maysave salt for next additional solution preparation. Accordingly, theFO&WS cleaning procedure according to the present invention isecologically friendly.

Residual Brine 28 is collected during previous FO&WS cleaning sessionsin tank 65. Residual brine 28 may be filtrated by micronics filter 54and may be added to tank 52 for re-concentration. Tank 52 comprises of awall 55. Wall 55 does not reach the bottom of tank 52. Wall 55 startfrom an about a height of 50 mm above the bottom of tank 52 allowingwater to flow and circulate below it but prevents dry slat to fill Pump53 suction compartment. Pump 53 circulates the additional solution forthe purpose to re-concentrate it until its saturation level. Dry salt 56is loaded into tank 52. During the additional solution circulation, theadditional solution passes gaps 61 between one or several magnets 58 and59. In accordance to one aspect of the invention, magnetic treatmentbased on permanent magnets may be made of FeNdB, NdFeB, Neodymium (Nd),Dysprosium (Dy), or Praseodymium (Pr) having for example 0.5 to 10Tesla.

In accordance with an embodiment of the invention a magnetic treatmentdevice 400 may consist of a tower of multiple magnets allowing water topass through their magnetic field. According to one embodiment, twotypes of magnets may be used. Ring shape magnets 58 with plugged holes,and ring shape magnets 59 with holes and peripheral plugs. These magnetsmay be arranged in pipe 60 in such a way that gaps 61 between adjacentmagnets is created and water may pass one magnet through it internalhole and the next magnet from the outside.

Gaps 61 between adjacent magnets are the areas where the magnetic field57 is the strongest. During dissolution of the dry salt and after itsdissolution, the additional solution 24 may be circulated continuouslyvia the magnetic treatment device. According to one embodiment, chargingthe syringe pump 51 with the additional solution 24 should be madeimmediately before the additional solution 24 is to be fed into themembrane module 100 during FO&WS cleaning procedure.

This magnetic treatment device increases the osmotic coefficient andactual osmotic pressure of additional solution 24.

The mechanical shaking of the membrane with periodic feeding ofadditional solution to the feed side of the membrane as described withreference to FIGS. 1 to 7 is carried out periodically, such as once aday for approximately 10 seconds. It does require a temporary halt inthe reverse osmosis process but provides enhanced fouling detachment andhence, cleaning of the membrane.

In an alternative embodiment of the present invention, cleaning may becarried out all the time with no feeding of additional solution (AS) tothe feed side. In this embodiment, known as “KEEPING CLEAN PROCEDURE”(“KCP”), mechanical shaking of the free membrane portions to detachfoulant is again carried out by applying, for a predetermined period oftime, a plurality of directional pressure strokes PGp and/or PGr on thepermeate and/or residual brine membrane side. In addition, a pulse-wiseflow regime is applied in the residual brine stream to increase theshearing force to the membrane thereby achieving enhanced foulingevacuation.

In this embodiment, the pressure strokes are precisely synchronized withflow pulsation, preferably in the alternating sequence: PGr pressuredecreasing, shearing force increasing; PGp increasing; followed by PGrpressure increasing, shearing force decreasing, PGp pressure decreasing,thereby providing synergetic enhancement of fouling detachment andevacuation. The required cleaning effect is achieved when the freemembrane portions shaking provided by residual brine gauge pressure PGrsharp decrease is precisely synchronized with permeate gauge pressurePGp sharp increase and precisely synchronized with residual brine flowvelocity increase.

As a non-limiting example, precise synchronization may be reached byconnecting the water generator to a 3-way valve connected to theresidual brine stream, permeate stream and to drain. A flexiblediaphragm or sealed piston or similar means may be provided between thesynchronized streams. The 3-way valve may switch the water strokegenerator between two positions to provide the required sequence, asfollows:

Position 1: The 3-way valve opens brine flow to water stroke generatorcausing PGr decrease, shearing force increase and permeate pressure PGpincrease; and

Position 2: The 3-way valve closes brine flow and connects water strokegenerator to drain, causing PGr increase, shearing force decrease andPGp decrease.

FIG. 8 of the accompanying drawings illustrates one example of anapparatus for achieving the aforementioned Keeping Clean Procedure.Water stroke generator 600 has a moveable sealed piston 601. The piston601 may have an equal diameter in the residual brine and permeate sidesor have a different diameter on each side. One side of water strokegenerator 600 is connected to permeate pipeline 29 via pipeline 31. Theother side is connected to the residual brine stream 128 or to the drainvia a 3-way valve 602. The stroke generator may also be provided with avent 604. The 3-way valve 602 has an activator controlled by aProgrammable Logic Control (PLC) (not shown on FIG. 8). The activatorserves to change the 3-way valve position by the required frequency. The3-way valve is movable between two positions (Position 1 and 2 above)wherein in Position 1 valve 602 connects line 128 to the water strokegenerator 600 and disconnects drain line 610 and Position 2 whereinvalve 602 disconnects line 128 from the water stroke generator 600 andconnects the drain line 610 to it.

As shown in FIG. 8, the arrangement 701 has similar connections with themodification that one side of the water stroke generator 600 isconnected via pipeline 609 to feed line, or to interstate residual brinestream pipeline in multistage RO systems, or to residual brine pipeline28 instead of the permeate line 29. Osmosis separation modules 100 mayhave residual brine stream valve 603 which opens and closessynchronically with valve 602. Permeate exiting from the permeateenclosure may be throttled by valves 12.

Thus, during normal reverse osmosis process through the osmosisseparation module 100, the keeping clean procedure (KCP) is carried outwith the stroke generator 600 being switched between the two positionsby means of the 3-way valve 602, providing precise synchronization ofpressure and flow alteration. The frequency movement of valve 602between the two positions may be tuned in to the vicinity of freemembrane portions natural frequency for achieving constructive and/orbeating interference oscillation of said membrane portions measurable asincrease in residual brine stream turbidity. The pattern of movement maybe continuous, rotational or include fast movement when valve changesbetween positions with some holdback in each open position. The holdbackmay not be equal in Position 1 and Position 2.

For large flow modules, continuous operation of arrangement 700 may becombined with arrangement 701, and may be combined with continuousoperation of valve 603. Arrangement 700 and 701 may work synchronically,asynchronically or each of them alone. Several arrangements 700 and/or701 may be installed in different positions of large flow osmosismodules.

The aforementioned 3-way valve arrangement is one example only ofdifferent arrangements that may provide precise synchronization betweenPGr decrease, shearing force increase, PGp increase. Additional valvesmay be installed in the exit of the residual brine stream and/orpermeate stream synchronized with the water stroke generator forpulse-wise discharge of brine in large modules. Such a valve in the exitof the residual brine stream may operate alone, without strokegenerator; closing and opening residual brine for providing pulse-wiseflow. A single valve arrangement is likely to produce a reduced cleaningeffect than combined with the stroke generator but be better thanstandard continuous residual brine flow approach.

The pressure pulses PGr, and/or PGp synchronized “in phase” on feedand/or permeate sides respectively may provide “Constructive PressureWave Interference” or Beating Pressure Wave Interference with freemembrane portion resonance oscillations. To reach such effect, thefrequency of pressure pulses have to be tuned to value equal,proportional or close to natural frequencies of free membrane portions.

The beating phenomenon may be used as instrument of tuning gaugepressure pulsation frequency into vicinity of membrane portions naturalfrequency. Because the same membrane element may have different sizes offree portions membrane, beating phenomenon may take place in differentfrequencies and tuning gauge pressure pulsation frequency may berequired in wide range. Measurement of reject flow turbidity may be goodindicator for selection of the right frequency range.

The Keeping Clean Procedure that may be performed all the time may besubjected to an additional activity at periodic time intervals as partof the procedure or as an independent procedure. The additional cleaningactivity comprises a periodic osmotic backwash (POB) which may beperformed with or without oxidation. This activity is made on-linewithout stopping the feed pump, with very limited interruption in thenormal desalination process. The periodic osmotic backwash may take afew minutes and may be implemented daily or every few hours. Thebackwash may employ an extremely small amount of cleaning solution thatneed not be discharged after use.

The periodic osmotic backwash is based on high frequency (several timesa minute) changes from Reverse Osmosis (RO) to Forward Osmosis (FO).This is brought about without feeding of Additional Solution to the feedside of the membrane but rather involves extremely fast and precisesynchronized changes of the residual brine and permeate gauge pressures;decrease PGr, increase PGp and vice versa. In this respect, the processchanges from RO to FO when the sign of net driving pressure, defined bythe balance of osmotic and gauge pressures PGr, Por, Pop and PGp,changes.

The POB procedure is based on our new understanding that the processchange between Reverse Osmosis to Forward Osmosis may be extremely quickbased on simultaneously, opposite sign, change of gauge pressures PGrand PGp. A quick change may take place because the osmotic process doesnot have massive inertial parts, and therefore change in flow directionmay take place immediately. This is not the case if process changebetween Reverse Osmosis to Forward Osmosis is based on injection ofAdditional Solution and a change osmotic pressure from POr to POs. Thisprocess cannot be quick.

Additionally, the POB procedure is based on our further understandingthat the backwash process on the membrane may be extremely short intime, because the distance on which fouling has to be moved frommembrane surface may be few microns, if the shearing force of residualbrine increases precisely in these microseconds when both pressures PGrand PGp shack membrane in the same direction and backward flow ofpermeate take place.

Furthermore, field experiments that have been carried out demonstratethat dozens of fast and frequent changes back and forth between RO andFO and dozens of short backwashes are more effective in fouling removalthan one single change from RO and FO and one long backwash.

A non-limiting numerical example to show this POB process is as follows:NDP (FO or RO)=+PGr−POr−PGp+POpNDP (RO)=+12−3−1+0.1=+8.1 bar. Sign (+) means the process is RO.

Thus, the difference between Keep Clean Procedure (KCP) and the periodicbackwash procedure (POB) is in adding one-step: throttling permeateexiting from permeate enclosure, increasing permeate gauge pressure PGpuntil the NDP value become equal to zero. In non-limiting numericalexample, PGp increases from 1 bar to 9.1 bar.NDP (Neutral)=+12−3−9.1+0.1=0.0 barPrecisely synchronized directional strokes with oppose directed changeof pressure: PGp (between 11.5 and 12.5 bar and PGr (between 9.6 and 8.6bar) providing plurality of quick RO-FO-RO process changes.NDP (FO)=+11.5−3−9.6+0.1=−1.0 bar. Sign (−) means the process is FONDP (RO)=+12.5−3−8.6+0.1=+1.0 bar. Sign (+) means the process is RO

In an alternative embodiment, the quick back and forth movement ofpermeate across the membrane caused by changing the process between ROand FO as described above is enhanced by the inclusion of a strongoxidizing agent. This procedure is termed “Periodical Oxidation andOsmotic Backwash” (PO&OB) and involves the addition of another step,being to inject cleaning solution into the permeate enclosure,preferably before the permeate throttling step. PO&OB may be implementedfor membranes such as graphene, zeolite, carbon, ceramic,nanostructured, mix matrix etc. that are able to withstand a highconcentration of strong oxidizers.

Different types of cleaning-solutions may be used in the PO&OB process.Preferably, the cleaning solution is able to pass via semipermeablemembrane in both directions. A non-limiting example of a suitablecleaning solution is a high concentration of oxygen dissolved in waterfor organic fouling removal, or a high concentration of carbon dioxidedissolved in water for calcium carbonate scaling removal.

The PO&OB cleaning of membrane requires a hundred-fold less amount ofchemicals compared to standard CIP process, where chemical solutioncirculates in feed-brine stream, external piping, CIP tanks, filters,and pumps.

Such a small amount of cleaning solutions is enough because the cleaningsolution is located only in small permeate spacer area, not circulatingthrough the system; it only goes back and forth in the distance of fewmicrons passing the membrane. Most of cleaning solution may be directedback after cleaning session into the same tank from which it wasinjected for cleaning. This repeated use of chemicals is possiblebecause cleaning solutions acts in feed membrane side when it is in FOmode and cleans itself when it is coming back through membrane in ROmode.

The POB may include implementation of cleaning solution PO&OB as option.The six steps POB procedure with PO&OB option, presented below isnon-limiting example. It uses the same water stroke generator, and thesame 3-way valve Position 1 and 2 that is presented in the previousembodiment “KCP” and shown in FIG. 8.

Step 1 (option with cleaning solution PO&OB): Cleaning solution injectedin one side of permeate enclosure and fill it up, when separation moduleis in normal RO operation.

Step 2: Throttling permeate exiting from permeate enclosure. ReachingNDP (Neutral).

Step 3: The 3-way valve in Position-1 opens brine flow to water strokegenerator, causing: PGr decreasing; PGp Increase. Process changed fromReverse Osmosis to Forward osmosis. Backwash by permeate takes place andfouling evacuation by high shearing force. (Fouling oxidizes ordissolves option PO&OB).

Step 4: The 3-way valve in Position-2 closes brine flow and connectswater stroke generator to drain. PGr increasing due to water hammercaused by sudden valve closing; permeate pressure PGp decreasing, causedby sudden opening brine side of water stroke generator to drain;Shearing force in feed membrane side decreasing. Process changed fromForward osmosis to Reverse Osmosis. Permeate goes back to permeate area.In PO&OB option chemical solution filtrate itself by this back movementvia membrane.

Steps 3 and 4 are repeated frequently causing “back and forth” dozens oftimes backwash and, optionally, dozens of fouling oxidation, or scalingdissolution.

Step 5 (option with cleaning solution PO&OB): Cleaning solution movesback to storage tank for re-concentration and reuse.

Step 6: Permeate enclosure opens by valve and begin normal RO operation.

Practical implementation of POB procedure may request two fieldadjustments for each specific osmosis separation module. The firstadjustment is throttling permeate exiting from permeate enclosure, forreaching NDP neutral. Although the value of PGp equal to neutral NDP maybe calculated, it worth to make some variation around this value, untilmaximum increase of brine turbidity may be measured. The secondadjustment is tuning frequency of pressure stroke alteration intovicinity of free membrane portions natural frequency also measurable asincrease in residual brine stream turbidity.

In accordance with one embodiment of the invention for heavy foulingcondition, shearing force may be increased even more if other waterstroke generators will be installed in residual brine line betweenstages of osmosis separation modules and/or outlets from them, withmodification, that instead of permeate line, the residual brine linewill constantly be connected to it.

Thus, the embodiment of the invention shown in FIG. 8 may be carry outdifferent cleaning operations, either continuously or at predeterminedtime intervals. Osmotic separation module 100 performs normal reverseosmosis process, which may include as non-limiting example severaloptions of operation:

Option A. Normal RO process which may include Keeping Clean Procedure.

Option B. Normal RO process which may include Keeping Clean Procedureand intermittently applied “Periodical Osmotic Backwash”

Option C. Normal RO process may include Keeping Clean Procedure, andintermittently applied “Periodical Osmotic Backwash” and some of“Periodical Osmotic Backwash” may be performed as Periodical Oxidation &Osmotic Backwash” (PO&OB).

Each of mentioned above procedure KCP, POB and PO&OB may be combined asdescribed above or applied as separate procedure in any configuration.

The six steps below presents POB and PO&OB procedure. The steps requiredfor PO&OB procedure marked (option PO&OP):

Step 1 (option PO&OP): Cleaning solution 606 injected from tank 605 andfills up permeate enclosure 29.

Step 2: Valve 12 throttles permeate exiting from permeate enclosure 29.Pressure PGp increases until neutral net driving pressure NDP reached.

Step 3: The 3-way valve 602 in Position-1 opens residual brine stream 28exiting from the module 100 towards water stroke generator 600 causingprecise synchronically: PGr decreasing; PGp increase, increasingshearing force 3, and providing short FO process.

Step 4: The 3-way valve 602 in Position-2 closes brine flow from line28, and connect water stroke generator to drain 610. PGr increasing dueto water hammer caused by sudden valve 602 closing; permeate pressurePGp decreasing, caused by sudden opening brine side of 3-way valve 602to drain 610. Precise synchronically PGr increase; PGp decrease provideshort RO process. Shearing force 3 in feed membrane side decreasing.Permeate goes back to permeate area. (Option PO&OP chemical solutionfiltrate itself by this back movement via membrane).

Steps 3 and 4 repeated frequently causing “back and forth” dozens oftimes changes RO-FO-RO process, and backwash. If cleaning solutionoption included dozens of fouling oxidation, or scaling dissolution willtake place.

Step 5 (option PO&OP): Cleaning solution 606 moves back to storage tank605 for re-concentration and reuse.

Step 6: Valve 12 opens module 100 returns to normal RO operation.

POB and PO&OB cleaning in addition to mentioned above KCP procedureexecutes:

Enhanced foulant detachment and evacuation due to applying pluralityquick RO-FO-RO backwash procedures,

Enhanced fouling oxidation and scaling dissolution due to applyingchemical treatment of fouling during plurality cleaning solutionpenetration via membrane in RO-FO-RO process,

Enhanced foulant evacuation may have more technological benefits such asincrease in recovery of separation module operation.

Arrangement 701 intended to provide plurality of directional pressurestrokes in residual brine stream between stages of osmotic separationmodules by using remainder pressure of final residual brine stream, andapplying pulse-wise flow regime to increase shearing force achievingenhanced fouling evacuation. In some applications arrangement 701 mayuse pressure in residual brine for pulse-wise pumping in separationmodule raw saline solution to, increase-shearing force.

The invention claimed is:
 1. A method for cleaning a semi-permeablemembrane in an osmosis separation module, said membrane having a feedside and permeate side with foulant located on at least the feed side, araw saline solution feed stream exiting the module as a residual brinestream, part of a raw saline solution from the raw saline solution feedstream penetrating the membrane in a reverse osmosis process by a netdriving pressure of a balance of gauge and osmotic pressures and exitingfrom the permeate side as a permeate stream, said cleaning methodcomprising: applying at least periodically, a plurality of directionalpressure strokes directed from at least one of the permeate and residualbrine stream to the feed stream side of the membrane thereby effectingmechanical membrane shaking for detachment of the foulant; and for atleast part of said period of time, applying a pulsed flow regime in atleast one of the residual brine and permeate stream exiting from themodule thereby increasing shearing force for achieving enhanced foulantevacuation wherein the plurality of directional pressure strokes aredirected from both the permeate and residual brine stream to the feedstream side of the membrane thereby effecting mechanical membraneshaking for detachment of the foulant; and wherein the pulsed flowregime is applied in both the residual brine and permeate stream exitingfrom the module thereby increasing shearing force for achieving enhancedfoulant evacuation.
 2. A method according to claim 1, further comprisingperiodically feeding said feed side of the membrane, an AdditionalSolution (AS) having an osmotic pressure POs, the osmotic pressure POsbeing greater than the osmotic pressure POr of the raw saline solutionthereby creating a net driving pressure that is opposite to reverseosmosis (RO), thereby inducing a forward osmosis (FO) process to createbackward flow of permeate towards the feed side, so as to lift saidfoulant.
 3. A method according to claim 1 wherein the semi-permeablemembrane includes at least one permeate spacer and the method furthercomprises mechanical membrane shaking at the natural frequency by tuningof the gauge pressure stroke PGp and/or PGr in a frequency between 0.1to 5 Hz until an increase in turbidity of the residual brine stream isvisible.
 4. A method according to claim 1 wherein the permeate streamhas a gauge pressure PGp and the permeate backward flow is induced byproviding a PGp within 4 bars of a minimum net positive suction head(NPSH) value of osmotic pump, being defined as the minimum PGp belowwhich backward flow is diminished.
 5. A method according to claim 1wherein the plurality of directional pressure strokes are provided byone or more of the following: a generator of pressure strokes installedin the residual brine stream which is configured to release and stopreleasing residual brine stream; and a generator of pressure strokesinstalled in the permeate stream which is configured to release and stopreleasing permeate flow from a permeate enclosure.
 6. A method accordingto claim 1 further comprising synchronization of permeate PGp andresidual brine PGr pressure strokes to create a net driving pressurethat is opposite reverse osmosis (RO), thereby inducing a forwardosmosis (FO) process to create flow of permeate towards the feed side,so as to lift said foulant.
 7. A method according to claim 6 furthercomprising throttling at least one of raw saline solution input andpermeate stream outlet until the NDP value becomes equal to zero andapplying thereafter synchronized directional pressure strokes PGp and/orPGr thereby providing a plurality of RO-FO-RO process changes.